Project 5 focuses on the ability of RGS (Regulators of G protein Signaling) proteins, enriched in the nucleus accumbens (NAc) and specific hypothalamic nuclei, to regulate mood and motivational state. RGS proteins sharpen responses of G protein-coupled receptors by serving as GTPase-activating proteins for G protein ai and aq subunits, and as scaffolding proteins that coordinate the assembly of receptors, G proteins, and effectors into macromolecular complexes. We have identified several specific subtypes of RGS proteins, enriched in the NAc or in specific hypothalamic nuclei (including those enriched in BDNF-the focus of Project 2, the peptides discussed in Project 3, and the circadian genes discussed in Project 4), which regulate drug reward and feeding behavior. Our hypothesis, now supported by considerable evidence, is that these various RGS proteins represent critical control points for the functioning of these neurons and thereby contribute to the regulation of mood and motivational. The goal of the proposed studies is to better understand the cellular localization of these RGS proteins within the brain's appetitive neural circuits and establish the behavioral phenotype subserved by these proteins. This work will rely on mice lacking a particular RGS protein and on viral-mediated gene transfer in rats. We will focus on a representative member of two of the three major subfamilies of RGS proteins that are enriched in these neural circuits and show interesting functional and regulatory properties, namely, RGS9 and RGS16. This focus will be extended to additional RGS subtypes of interest in future grant proposals. In addition, we will characterize the regulation of these RGS proteins by stress and antidepressant treatments, as well as by circadian rhythms and feeding, which we have documented in preliminary investigations. We also will explore a role for CREB in mediating these effects. Furthermore, we are interested in understanding the influence these RGS proteins play, as proximal modulators of receptor signaling, in controlling the activity of other signaling proteins expressed in these neurons that are of interest to this Center.